Ultrasound used to stimulate tactile sensations in brain

Scientists have provided the first neurophysiological evidence for something that medicos have long suspected: ultrasound applied to parts of the body, such as the fingertips, can stimulate different sensory pathways leading to the brain. The researchers, from Virginia Tech, say the discovery has implications for diagnosing and treating neuropathy, which affects an estimated 20 million people in the United States alone. The breakthrough could also find its way into applications ranging from surgery to consumer electronics.

Neuropathy is a collection of nervous system disorders that may cause pain, numbness, and sensations of burning, itching, and tingling. One of the most common causes of neuropathy is Type 2 diabetes. Autoimmune disorders, traumatic nerve injury; genetic abnormalities; movement disorders; and infectious diseases can also trigger neuropathy.

“Neuropathy involves both motor nerves that control how muscles move and sensory nerves that receive sensations such as heat, pain, and touch. Ideally, neurologists should be able to tailor treatments to the specific sensations their patients are feeling,” said William “Jamie” Tyler, who led the study that appears in PLOS ONE. “Pulsed ultrasound allows us to selectively activate functional subsets of nerve fibers so we can study what happens when you stimulate, for example, only the peripheral fibers and central nervous system pathways that convey the sensation of fast, sharp pain or only those that convey the sensation of slow, dull, throbbing pain.”

The researchers used functional magnetic resonance imaging (fMRI) and electroencephalography (EEG) to provide physiological proof of their observations. Study participants rested their index fingers on ultrasound transducers while having their brain activity monitored with fMRI and EEG. The scientists found that they could stimulate specific sensory pathways just by tweaking the ultrasound waveforms.

The discovery could lead to a host of other applications. “Ultrasound transducers could be fashioned into flexible, flat insoles to provide sensory stimulation to people who have lost sensation in their feet, including the elderly, who are at such risk of falling,” he speculated. “Surgical instruments could provide tactile feedback to surgeons in training. And I can imagine countless applications for consumer electronics. Users already rely on two-way somatosensory communication with their devices, and peripheral stimulation using ultrasound could add new dimensionalities to this.”

The researchers now plan to investigate which ultrasound parameters stimulate which types of nerve fibers or receptors. Tyler also hopes to study people with Type 2 diabetes who have not yet developed neuropathy, with the ultimate goal of providing clues to treating or even preventing the pain associated with the condition.